1. Field of the Invention
The present invention relates to an inkjet recording apparatus and an image forming method, and more particularly, to an image forming technology using ultraviolet-curable ink.
2. Description of the Related Art
Conventionally, an inkjet recording apparatus which forms a desired image on a recording medium by ejecting color ink from an inkjet head is known as a general image forming apparatus. In recent years, non-permeable (low-permeability) media such as resin film have been used, in addition to media having permeability, such as paper, and apparatuses which cure ink deposited on a medium by irradiating ultraviolet light as active light have been proposed. The ultraviolet-curable ink used in this apparatus contains a photoinitiator having prescribed sensitivity with respect to ultraviolet light.
In an inkjet recording apparatus which uses ultraviolet-curable ink, a light source for irradiating ultraviolet light is mounted on a carriage on which an inkjet head is installed, the ultraviolet light source is scanned (moved) so as to follow the inkjet head, and ultraviolet light is irradiated onto ink droplets immediately after landing on a medium, thereby preventing positional displacement of the ink droplets.
U.S. Pat. No. 7,600,867 discloses an ultraviolet-curing type of print system in which curing light sources arranged on either side in the main scanning direction of an inkjet head are composed movably on the downstream side of the conveyance direction of the recording medium. The print system described in U.S. Pat. No. 7,600,867 semi-cures ink droplets by irradiating ultraviolet light of a low amount immediately after landing of the ink droplets, and after a prescribed period of time has elapsed, moves the curing light source to the downstream side of the inkjet head in terms of the conveyance direction of the recording medium and then performs main curing of the ink droplets by irradiating ultraviolet light of a high amount.
However, in image formation in which layers of color ink, a layer of white ink and a layer of clear (transparent) ink are superimposed on each other on a recording medium, the activation energy absorption characteristics (ink curing characteristics) vary with differences in the inks, and therefore curing defects due to insufficient activation energy and image defects due to excessive activation energy may occur.
The print system described in U.S. Pat. No. 7,600,867 varies the amount of light in provisional curing and main curing, but the amount of light irradiated onto all of the inks is uniform. In other words, in image formation in which layers of color inks and a layer of white ink or clear ink are stacked together, it is difficult to resolve the aforementioned problems caused by differences in the ultraviolet light absorption characteristics of the respective inks.